Syntheses and Characterization of Novel Three-Dimensional Tellurites, Na2MTe4O12 (M = W, Mo), with Intersecting Tunnels

Two isostructural tellurium-rich tellurites, Na 2 WTe 4 O 12 ( 1 ) and Na 2 MoTe 4 O 12 ( 2 ), have been synthesized and structurally characterized by single-crystal X-ray diffraction studies. Three types of polyhedra, namely, MO 6 octahedra, TeO 3 pyramids, and TeO 5 square-pyramids, constitute the three-dimensional (MTe 4 O 12 ) 2 - (M = W, Mo) anionic framework, which contains different types of intersecting tunnels, one of them being novel spiral pseudohexagonal tunnels occupied by sodium ions. Both compounds have the monoclinic space group C 2/ c, with Z = 4. The lattice parameters are as follows: for 1, a = 17.348(3) Å, b = 5.7755(10) Å, c = 11.269(3) Å, β = 104.33(2)°; for 2, a = 17.341(4) Å, b = 5.8262(11) Å, c = 11.268(2) Å, β = 104.38(2)°. Syntheses and structure, powder X-ray diffraction, and infrared spectroscopic studies of these compounds are described.